United States 

Department of Agriculture 

Office of 

the Chief Economist 

Office of Energy Policy 

and New Uses 

Agricultural 

Economic 

Report 

Number 845 

September 2009

Energy Life-Cycle Assessment 

of Soybean Biodiesel 

A. Pradhan 

 

D.S. Shrestha 

 

A. McAloon 

 

W. Yee 

M. Haas 

J.A. Duffield 

H. Shapouri 
Table of Contents 

Summary..................................................................................................................................... iii 

Energy Life-Cycle Assessment of Soybean Biodiesel................................................................1 

Methodology .................................................................................................................................2 

Data Description and Trends......................................................................................................3 

Energy Life-Cycle Inventory ......................................................................................................7 

Feedstock Production ..................................................................................................................7 

Estimating Energy for Transporting Soybeans to Biodiesel Plant..........................................8 

 Estimating Energy for Oil Crushing and Biodiesel Conversion..............................................9 

 Oil Extraction From Soybeans..............................................................................................9 

 Conversion of Soybean Oil Into Biodiesel..........................................................................10

Biodiesel Transport....................................................................................................................12 

Calculating Energy Coproduct Values ....................................................................................12 

Results.........................................................................................................................................14 

The Effects of Adding Inputs to the LCI .................................................................................15 

 The Effect of Adding Lime to the LCI .................................................................................16

 Effect of Oil Transport ........................................................................................................16

Effect of Soybean Yield..............................................................................................................17 

Summary and Conclusion .........................................................................................................17 

References...................................................................................................................................18 

Appendix ....................................................................................................................................21 

Glossary .....................................................................................................................................22 

i 
About the Authors 

A. Pradhan is a graduate student and D. Shrestha is an assistant professor in the Department of 

Biological and Agricultural Engineering, University of Idaho. 

A. McAloon is a cost engineer, W. Yee is a chemical engineer, and M. Haas is a lead scientist at 

the Eastern Regional Research Center in USDA’s Agricultural Research Service. 

J.A. Duffield and H. Shapouri are agricultural economists in the Office of Energy Policy and 

New Uses in USDA’s Office of the Chief Economist. 

Acknowledgements 

The authors would like to thank all the reviewers and others who provided useful comments on 

this report. In particular, we would like to thank Mark Ash, Bill McBride, Gary Knothe, Jim 

Pollack, and Michael Wang for their suggestions, which significantly improved the study. 

This report is available on the Web at: http://www.usda.gov/oce/global_change/index.htm

Printed copies may be purchased from the National Technical Information Service. Call 1-800-553-NTIS 

(6847) or 703-605-6000, or visit: http://www.ntis.gov. 

ii 
Summary 

The first comprehensive life-cycle inventory (LCI) for biodiesel produced in the United States 

from soybean oil was completed by Sheehan et al. in 1998. The purpose of the study was to 

conduct a life-cycle assessment (LCA) to quantify and compare the environmental and energy 

flows associated both with biodiesel and petroleum-based diesel. One of the most often cited 

results from Sheehan et al. is that the fossil energy ratio of biodiesel is equal to 3.2. In other 

words, biodiesel yields 3.2 units of energy for every unit of fossil energy consumed over its lifecycle. By contrast, it was found that petroleum diesel’s life cycle yielded only about 0.84 units 

of energy per unit of fossil energy consumed. The purpose of the following analysis is to update 

the energy life cycle of the model to determine if any significant changes in the original 

inventory have occurred since the model was first developed 10 years ago. 

The LCI of biodiesel in this analysis includes four subsystems: feedstock production, feedstock 

transportation, soybean processing with biodiesel conversion, and product distribution. All 

significant sources of energy are included in the inventory, such as the liquid fuel and electricity 

used to directly power equipment in the system. The energy requirements to produce materials 

that are made from energy resources, such as fertilizers, pesticides, and other petrochemicals, are 

also included in the inventory. The soybean crushing model in this analysis uses the hexane 

extraction method to extract oil from soybean seed, and transesterification is used to convert 

soybean oil into biodiesel. Oil extraction and transesterification result in the production of two 

important coproducts, soybean meal and crude glycerin, respectively. A mass-based allocation 

method is used to account for the energy associated with the soybean meal and crude glycerin. 

The fossil energy ratio (FER), which is used in this study to measure the energy balance of 

biodiesel, is defined as the ratio of the energy output of the final biofuel product to the fossil 

energy required to produce the biofuel. The energy requirements of biodiesel include all the 

fossil energy in the LCI and do not include any renewable energy, such as solar or hydroelectric 

energy. The analysis first constructed a base case, in which the inventory was kept basically the 

same as the inventory used in the Sheehan et al. report. Then additional inputs that were 

excluded by Sheehan et al., such as agricultural machinery and energy embodied in building 

materials, were added to study their impact on the FER. 

The Sheehan et al. study used data from a U.S. Department of Agriculture (USDA) conducted 

survey on soybean production in 1990, and this study used data from a 2002 USDA survey. 

Given the long time period between surveys, the newer data would be expected to reflect some 

changes in soybean production practices over time. One major change that has occurred is the 

increased adoption of no-till practices by soybean farmers, which reduces fuel requirements. 

Another change is the widespread adoption of genetically engineered (GE) soybeans, which have 

had a major effect on pesticide use. Soybean yields have been improving over time because of 

new seed varieties, improved fertilizer and pesticide applications, and new management 

practices. Energy savings have also occurred in the soybean crushing industry because facilities 

that have been built in recent times are far more energy efficient than the older plants. 

iii 
The first subsystem constructed for the LCI was soybean production, which is the feedstock 

source for the biodiesel examined in this study. Energy requirements for producing soybeans 

were estimated for both direct energy, such as diesel fuel, and gasoline, and indirect energy, such 

as fertilizers and pesticides. Diesel fuel use required the most energy on the farm, followed by 

fertilizers, and herbicides. Next, the energy required to transport soybeans from the farm to 

processing plants was estimated based on information from the Greenhouse Gases, Regulated 

Emissions, and Energy Use in Transportation (GREET) Model. It requires about 6,393 British 

Thermal Units (Btu) to transport 1 bushel of soybeans to a processing facility. 

The model used in this study was designed to represent a processing facility that combines a 

soybean processing plant with a biodiesel conversion unit producing 9.8 million gallons of 

biodiesel, 151,515 tons of soybean meal, 9,000 tons of soybean hulls, and 4,380 tons of crude 

glycerin. The soybean crusher uses energy in the form of electricity to power motors and 

provide lighting. Natural gas and process steam are used to provide heat for drying. Hexane is 

used for oil extraction. The total amount of energy required for removing the soybean oil is 

about 23,000 Btu per gallon of biodiesel. The soybean oil is converted into biodiesel using a 

process called transesterification, which is done by reacting the oil with an alcohol and a catalyst 

in large reactors. This reaction also results in the production of crude glycerin, which is a 

valuable coproduct. The conversion of the soybean oil into biodiesel and the treatment of the 

glycerin requires almost 19,000 Btu per gallon of biodiesel. Energy is also required to ship the 

biodiesel from the processing plant to marketing outlets. Using the GREET model, it was 

determined that on average it requires about 1,000 Btu to ship a gallon of biodiesel to its final 

destination. 

Combining the energy input estimates from the four subsystems completed the base case lifecycle assessment for biodiesel. After adjusting the energy inputs by energy efficiency factors 

and allocating energy by coproducts, the total energy required to produce a gallon of biodiesel 

was 25,696 Btu. Biodiesel conversion used the most energy, accounting for about 60 percent of 

the total energy required in the life-cycle inventory. Soybean agriculture accounted for 18 

percent of the total energy requirements, followed by soybean crushing, which required almost 

15 percent of the total energy. The net energy value (i.e., biodiesel energy output, minus fossil 

energy input) was about 91,000 Btu per gallon. The estimated FER of biodiesel was 4.56, which 

is about 42 percent higher than the FER reported by Sheehan et al. 

The next step in this analysis was to add secondary energy inputs to the LCI that were not 

included in Sheehan et al. to determine how they affect the overall results. The secondary inputs 

added were farm machinery, building materials for a crushing plant, and building materials for a 

biodiesel conversion plant. When the input energy for both agricultural machinery and building 

material are added to the inventory, FER declines to 4.40, still considerably higher than the 3.2 

FER reported by Sheehan et al. In addition, Sheehan et al. omitted lime from their LCI, whereas 

this study included lime in the base case LCI. However, lime use only accounted for about 500 

Btu per bushel of soybeans, and adding it to the LCI only lowered the FER by 0.22 percent. 

The final step in this analysis was to examine the effect of rising soybean yields on the FER of 

biodiesel. The analysis found that the FER of soybean biodiesel is expected to reach 4.69 when 

projected soybean yield reaches 45 bushels per acre in 2015. This is about a 3-percent increase 

iv 
v 

compared to the 2002 FER estimate. This result suggests that the FER of biodiesel will continue 

to improve over time. In addition to higher yields, improvements can be expected to occur in 

other areas of the life cycle as the agricultural sector, along with the biodiesel industry, continues 

to make energy efficiency gains in order to lower production costs. 
Energy Life-Cycle Assessment of Soybean Biodiesel 

A. Pradhan, D. S. Shrestha, A. McAloon, W. Yee , M. Haas, J. A. Duffield, and H. Shapouri 

Much of the attention directed toward renewable fuels, such as biodiesel, is focused on the 

perception that they have superior environmental properties compared to their petroleum fuel 

counterparts (U.S. Environmental Protection Agency, 2002; Knothe et al.). In addition, 

developing renewable fuels is desirable because they are derived from sustainable sources of 

energy, whereas petroleum fuels come from a finite resource that is rapidly being depleted. 

However, the production of renewable fuels generally involves a significant amount of fossil 

energy (e.g., petroleum-derived diesel fuel is used to cultivate and harvest the soybeans used to 

make biodiesel). The amount of fossil energy used for biodiesel must be measured over the 

entire life cycle of biodiesel production to determine the extent to which it depends on petroleum 

fuels. The degree to which biodiesel is renewable is largely a factor of the amount of fossil 

energy used for its production. 

It is beneficial to know the renewability of a biofuel for two reasons. First, it is useful to know 

how much a biofuel relies on petroleum-derived energy for its production; the less a biofuel 

depends on petroleum energy, the more potential it has for diversifying our total fuel supply. 

Secondly, the renewability factor is one of many criteria that may be used by policymakers and 

others to evaluate and compare various biofuels. Renewability is a useful measurement that can 

be used along with other measurements, including environmental, economic, and social criteria, 

to assess the benefits of biofuels. 

In 1998, the first comprehensive life-cycle inventory (LCI) for biodiesel produced in the United 

States from soybean oil was completed by Sheehan et al. The inventory and model assumptions 

were developed by a large stakeholders group and several peer reviewers, including experts from 

numerous disciplines and institutions. The purpose of the study was to conduct a life-cycle 

assessment (LCA) to quantify and compare the environmental and energy flows associated both 

with biodiesel and petroleum-based diesel. The LCI flows examined included greenhouse gases, 

energy use, and other air emissions. Other biodiesel LCAs have been done since Sheehan et al., 

but none have matched the detailed information or collaborative effort used to produce the 

original report (Hill et al. and Huo et al.). 

One of the most often cited results from Sheehan et al. is that the fossil energy ratio of biodiesel 

is equal to 3.2. In other words, biodiesel yields 3.2 units of energy for every unit of fossil energy 

consumed over its life cycle. By contrast, it was found that petroleum diesel’s life cycle yielded 

only about 0.84 units of energy per unit of fossil energy consumed. The purpose of the following 

analysis is to update the energy life cycle of the model to determine if any significant changes in 

the original inventory have occurred since the model was first developed 10 years ago. For 

example, the adoption of new technologies in the farm sector, the soybean processing sector, and 

in the biodiesel industry are expected to affect life-cycle energy use. 

1 
 Methodology 

 

Following Sheehan et al., the formula used in this study to estimate the fossil energy ratio (FER) 

is defined in equation 1: 

FER

Energy Fossil Input

Energy Fuel Renewable Output  . (1) 

A biofuel’s FER is defined as the ratio of the energy output of the final biofuel product to the 

fossil energy required to produce the biofuel. The FER as defined above only includes fossil 

energy in the denominator. For example, it does not include the energy value of the soybeans 

used to make biodiesel, and it does not include any solar or hydroelectric energy because these 

sources of energy are renewable. 

Estimating FER begins with defining the entire production system of biodiesel, which includes 

four subsystems in this analysis: feedstock production, feedstock transportation, soybean 

processing with biodiesel conversion, and product distribution. An inventory is then developed 

that identifies and quantifies all the fossil energy inputs used in each subsystem. All significant 

sources of energy are included in the inventory, such as the liquid fuel and electricity used to 

directly power equipment in the system. The energy content of materials that are made from 

energy resources, such as fertilizers, pesticides, and other petrochemicals, is also included in the 

inventory. The energy values of all fossil energy used in the system are adjusted by energy 

efficiency factors to take into account the energy used to convert fossil resources into usable 

energy (table A2). The energy efficiency factors also adjust for any energy required to mine, 

extract, and manufacture the raw energy sources. Estimates of electricity generation used 

throughout the life cycle are based on the U.S. weighted average of all sources of power, 

including coal, natural gas, nuclear, and hydroelectric. About 70 percent of the electricity 

generated in the United States comes from fossil fuel (Energy Information Administration); 

hydroelectric and other nonfossil sources provide about 30 percent. The efficiency of electricity 

generation in the U.S. increased from 32 percent as reported in Sheehan et al. to 33.71 percent in 

2007 based on data from the Energy Information Administration. In addition to generation loss, 

there is also a loss of electricity over the distribution lines, which reduces the overall efficiency 

of electricity to 31.29 percent. Therefore, all electricity used over the life cycle is increased by a 

factor of 3.2 to account for generation and distribution losses. 

Similarly to Sheehan et al., the soybean crushing model in this analysis uses the hexane 

extraction method to extract oil from soybean seed, and transesterification is used to convert 

soybean oil into biodiesel. Oil extraction and transesterification result in the production of two 

important coproducts, soybean meal and crude glycerin respectively. Since this energy life cycle 

focuses exclusively on biodiesel, the energy associated with the production of the other two 

coproducts must be estimated and excluded from the inventory. Since detailed information is 

often not available to measure the exact energy requirements of the individual coproducts, an 

allocation method can be used to assign coproduct values. There are several allocation methods 

that can be used to estimate the energy value of coproducts. For example, the energy method 

uses the energy content of each coproduct to allocate energy. Another example is the economic 

method, which uses the relative market value of each coproduct to allocate energy. Sheehan 

2 
et al. used a mass-based allocation method, and to be consistent with their analysis, this study 

also uses the mass-based allocation method. In general, no allocation method is always 

applicable, and the appropriate method should be chosen on a case-by-case basis. For more 

discussion on allocation methods, see Shapouri et al. 

The mass-based allocation method is commonly used because it is easy to apply and provides 

very reasonable results (Vigon et al., 1993). This method simply allocates energy to the various 

coproducts by their relative weights. This allocation rule separates the energy used to produce 

the soybean oil from the energy used to produce the soybean meal and glycerin in the following 

manner: 

Energy input allocation for biodiesel = E1 f1 + E2 f2 + E3 (2) 

where E1 is energy input for agriculture, soybean transport and soybean crushing, f1 is the mass 

fraction of soybean oil used to produce biodiesel; E2 is the energy used during transesterification 

and the transport of the soybean oil, and f2 is mass fraction of the transesterified oil used to 

produce biodiesel. E3 is energy input for biodiesel transport. 

Over the past several years, the FER, also called energy balance, of soybean biodiesel has been 

reported by different researchers with considerable variation in results (Hill et al.; Huo et al., and 

Pimentel and Patzek.). A major cause for the contradicting results is the difference in the amount 

of energy allocated between the soybean oil used to make biodiesel and the soybean meal. 

Historically, soybean demand is driven by the demand for soybean meal, which is used as a highprotein animal feed. Crushing soybeans yields considerably more meal than oil, as well as more 

revenue. Clearly, soybean meal is not a byproduct of biodiesel production. Rather, soybean 

meal and oil are jointly produced and sold in separate markets. Therefore, an allocation method 

must be used to determine how the energy used for crushing soybeans should be divided between 

the two products. Unfortunately, different allocation methods can produce significantly different 

coproduct energy values. For a detailed comparison and discussion of the different coproducts 

used in the literature, see Pradhan et al. 

Data Description and Trends 

At the time of the Sheehan et al. study, the most recent detailed data available on soybean 

production was from the U.S. Department of Agriculture’s (USDA) 1990 Farm Costs and Return 

Survey (FCRS). The FCRS, which was replaced by the Agricultural Resource Management 

Survey (ARMS) in 1996, is conducted annually, but to reduce survey costs, USDA does not 

undertake detailed surveys of every commodity each year. Thus, the ARMS covers a major 

commodity in detail about every 4 years, with the most recent survey conducted on soybeans in 

2006. This study, however, uses the 2002 data, because the 2006 data became available just prior 

to the release of this study. The ARMS soybean survey only covers major soybean producing 

States, and detailed data are only reported for a selected number of these States. In 1990, Statelevel estimates were available for 14 States and the 2002 soybean survey provided detailed Statelevel data on 20 States. These 20 States are responsible for 98 percent of the soybean production 

(table 1). The USDA uses other versions of the ARMS to gather annual data for national 

soybean production estimates, but they are limited compared to the ARMS soybean survey, 

3 
4 

which is the only USDA source that provides detailed data on machinery and fuel use. Data 

from the 2002 ARMS soybean survey on chemicals and fertilizers were not made available at the 

time of this study, so other USDA data sources were obtained (table 1). 

To stay competitive, U.S. farmers are continually minimizing their input costs and increasing 

productivity. Therefore, soybean data would be expected to reflect some changes in soybean 

production practices over time. One major change that has occurred is the increased adoption of 

no-till practices by soybean farmers. No-till use increased in soybean production from about 10 

percent of acreage in 1990 to about a third in 2000. Thus, significantly fewer soybean acres 

required fuel for tilling over this time period (USDA Economic Research Service [ERS], 2003). 

The most significant change in U.S. soybean production since 1990 is the use of genetically 

engineered (GE) soybeans, which have had a major effect on pesticide (includes herbicides, 

insecticides, and fungicides) use. The 1990 ARMS soybean production data used in the Sheehan 

et al. report did not include any GE soybeans because they had not been introduced into U.S. 

agriculture yet. However, by 2002 the rapid rise in GE soybeans had reached 75 percent of the 

soybeans planted, and today almost all soybeans in the United States are GE varieties (USDA 

ERS, 2007). Genetically engineered soybeans with herbicide-tolerant and pest-management 

traits increase yields through improved weed and pest control. Using GE soybeans also reduces 

pesticide use and costs (Heimlich et al., 2000). Based on data published in the National 

Agricultural Statistics Service’s (NASS) Agricultural Chemical Usage survey, over the 5-year 

period from 1990 to 1994; 1995 to1999; and 2000 to 2004, the average herbicide use was 1.18, 

1.11 and 1.09 lb/acre/year respectively (USDA, NASS, 1990-2005). However this average 

decrease in herbicide use may not be realized from year to year because annual pesticide use 

depends on the level of infestation. For instance, the insecticide application rate was higher for 

the years 2005 and 2006, mostly because of higher aphid infestation (Thorson). Some herbicides 

are also less toxic today. For example, most of the herbicide used on soybeans is now in the form 

of glyphosate, which is about 10 times less toxic in terms of the oral Reference Dose (RfD) 

established by the Environmental Protection Agency (EPA) than herbicides used in the past, such 

as Alachlor (EPA, 2008). Kovach et al. found that the environmental impact quotient (EIQ), 

which encompasses 11 different types of toxicity measurements and environmental impacts, was 

found more favorable for glyphosate (EIQ =15.3) than for alachlor (EIQ = 18.3). 
Table 1 – Soybean agriculture system inputs, major States, 2002 

State AR IL IN IA KS KY LA MD MI MN MS MO NE NC ND OH SD 

Input Seed lbs/ac 59.4 69.9 71.7 63.6 59.5 66.1 54.4 67.4 77.4 67.3 51.4 68.6 67.9 54.1 72.3 84.2 65.1 

Fertilizer  Nitrogen lbs/ac 1.76 3.55 3.00 0.89 4.44 7.44 0.13 5.51 11.9 2.24 2.57 2.34 4.91 10.6 16.5 2.97 7.65 

 Phosphorus lbs/ac 19.6 13.6 11.7 4.64 10.4 23.5 6.96 5.92 15.6 4.75 11.0 12.5 17.0 18.4 18.9 13.2 24.0 

 Potash lbs/ac 22.4 40.1 47.6 15.7 2.15 36.1 9.49 14.3 58.1 5.43 17.9 31.3 3.11 37.8 1.24 58.2 5.74 

Direct Energy  Gasoline gal/ac 1.3 0.90 1.60 1.10 1.10 1.40 1.10 2.10 1.50 1.10 1.20 1.40 1.30 1.50 1.40 1.30 1.40 

 Diesel gal/ac 9.90 2.50 2.30 3.40 2.90 2.10 6.50 2.90 4.00 4.00 4.30 4.30 12.9 2.40 3.20 2.00 2.80 

 Propane gal/ac NR 0.00 NR 0.00 1.80 NR NR NR NR NR NR NR 4.40 NR NR NR 0.00 

 Electricity kWh/ac 11.2 NR 1.30 0.00 9.10 4.50 NR 0.80 NR NR 3.80 NR 39.4 0.60 0.80 0.00 NR 

 Natural Gas Cf/ac NR 0.00 NR 0.00 349 0.00 NR 0.00 0.00 0.00 0.00 0.00 586 0.00 0.00 0.00 0.00 

Chemicals 

 Herbicides lbs/ac 1.00 1.23 1.35 1.26 1.07 1.15 1.60 1.54 1.22 0.98 1.66 1.17 1.28 1.00 1.26 1.34 1.20 

 Insecticides lbs/ac 0.04 0.00 0.00 0.01 0.00 0.00 0.60 0.34 0.00 0.00 0.02 0.00 0.01 0.07 0.00 0.00 0.02 

 Lime lbs/ac 53.7 595 668.8 286.4 146.7 865.6 70.7 NA 323.3 181.8 120 818.5 123.9 652.9 NR 394.6 NR 

Yield Bu/ac 33.5 43.0 41.5 48.0 23.0 33.0 32.0 23.0 38.5 43.5 32.0 34.0 38.5 24.0 33.0 32.0 31.0 

Source: USDA, National Agricultural Statistics Service (NASS), 2005; USDA, Economic Research Service (ER(b); and USDA, NASS, 2003. *Weighted by area harvested in each State. NR: Not reported in that State due to small sample size.

5 
Lime use was not reported by Sheehan et al.; however, farmers apply lime periodically to 

increase soybean yield. In 2002, the average lime application for soybean production was 2 tons 

per treated acre (USDA, ERS b). About 52 percent of the total planted acres were treated with 

lime, and the lime was applied on average every 5.9 years. Adjusting for the soybean planted 

acres and the annual rate, the lime application rate was estimated to be 358 pounds per acre. 

Soybean yields also have been improving over time because of new seed varieties, improved 

fertilizer and pesticide applications, and new management practices (Ash et al., 2006). The data 

show a significant increase in soybean yield since 1990 (figure 1). Soybean yields have 

increased steadily since 1990 when the U.S. average yield was 34.1 bushels per acre, and by 

2002, U.S. soybean yield increased to 38 bushels per acre (Ash and Dohlman). The latest USDA 

estimate for soybean yield is 41.7 bushels per acre for the 2007 crop year (USDA, Office of the 

Chief Economist-b). The data trend shows a continuous increase in yield but there was no 

significant increase in other agricultural inputs. Consequently, as shown later in this report, the 

FER increases with crop productivity. 

There have also been major changes in the soybean crushing industry that are expected to reduce 

the energy requirements of biodiesel. Unfortunately, the best data available to Sheehan et al. on 

oil crushing were based on a single facility that was 17 years old at the time of the study. 

Although adjustments were made to the model to modernize the plant, it is unlikely that it was a 

good representative of a typical crusher of the time. Thus, the typical plant in operation today is 

much newer than the plant modeled by Sheehan et al. For example, the oil extraction rate has 

increased since the Sheehan et al. study, which used 10.16 pounds per bushel (Table 79, pp 134). 

Figure 1  U.S. national average soybean yield 1980-2007 and expected trend to 2010 

25

30

35

40

45

1980 1985 1990 1995 2000 2005 2010

Yield (bu/acre)

Year

Source: Ash and Dohlman; and USDA, Office of the Chief Economist (b). 

6 
The oil extraction rate for crop year 2002/2003 was 11.39 pounds per bushel and increased to 

11.55 pounds per bushel in crop year 2007/2008 (USDA ERS, 2009). Even though the oil 

extraction rate for year 2007/2008 was higher, the oil extraction rate of 2002/2003 was used in 

this report to be consistent with the 2002 ARMS agricultural input data. Furthermore, newer 

plants are more energy efficient due to the adoption of energy saving technologies that reduce 

production costs. Process improvement in extraction plants has continued with increasing 

emphasis on energy efficiency, reducing hexane loss, and increasing capacity. For instance, the 

current acceptable level of solvent loss is one-third the level used by U.S. extraction plants in 

1970 (Woerfel). 

Likewise, the amount of energy required to convert soybean oil into biodiesel using 

transesterification may have decreased over the past decade if producers have adopted energysaving processing equipment to minimize production costs. The rise in larger biodiesel facilities 

with corresponding larger energy requirements has prompted greater emphasis on minimizing 

energy costs. The capital cost of adding energy saving technologies would be justified if the 

investment cost is less than the savings from lower energy costs. For example, heat integration 

technologies have resulted in the capture and reuse of heat that was previously discharged. 

Improvements in the catalytic technology used to produce biodiesel have resulted in higher 

conversion efficiencies of soybean oil into biodiesel. Reclaiming and reusing the wash-water 

stream used to purify biodiesel eliminates the need for wastewater treatment. 

Energy Life-Cycle Inventory 

This section describes the inventory and data used to construct the four subsystems of the 

biodiesel life cycle: feedstock production, feedstock transportation, soybean processing with 

biodiesel conversion, and product distribution. The analysis first constructs a base case, in which 

the inventory was kept basically the same as the inventory in the Sheehan et al. report. Then 

additional inputs that were not included in Sheehan et al., such as agricultural machinery and 

energy embodied in building materials, were added to study their impact on the FER. 

Feedstock Production 

The farm input data for soybean production were obtained from ARMS and the National 

Agricultural Statistics Service (NASS). The direct energy data came from the 2002 ARMS, 

which were the most recent soybean survey data available at the time of this study (table 1). The 

State soybean yield data are USDA estimates reported by NASS (USDA, NASS, 2005). The 

fertilizer and chemical data for year 2002 soybeans are from the USDA’s NASS Agricultural 

Chemical Survey. The lime-application rates and the seed-application rates shown in table 1 are 

State averages from the 2002 ARMS (USDA, ERS-a; and USDA ERS-b). 

The farm input data in table 1 were weighted by State acreage to derive average energy used for 

U.S. soybean production. The weighted average soybean yield for the State data equaled 38 

bushels per acre in year 2002. The weighted average energy input use and the weighted average 

yield were used to estimate the energy required to produce a bushel of soybeans in the United 

States (table 2). The direct energy inputs were converted to British thermal units (Btu) using 

low-energy heating values, assuming that electricity generation came from a combination of 

7 
coal, natural gas, nuclear, and hydropower at the same proportion as the national average. 

Electricity use only includes electricity generated from fossil sources, which on a national 

average equals 70 percent. The energy used for planting the seed and other farm activities, such 

as land preparation, plowing, weeding, fertilizer and pesticide application, irrigating, harvesting, 

and drying, is included in total farm fuels and electricity estimates. The fuel required for hauling 

the soybeans from the field to the first destination point, either farm storage or local market, is 

also included in the fuel estimates. The conversion factors used to convert farm energy inputs 

into Btus are listed in Appendix table 1. 

Estimating Energy for Transporting Soybeans to Biodiesel Plant 

The amount of energy required to transport soybeans to processing plants came from the 

Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) Model 

(Argonne National Laboratory). The energy required for transporting soybeans to processing 

Table 2 – Energy equivalents for base case soybean agriculture system inputs before 

allocating coproduct values, 2002 

 

20 StatesWeighted 

Inputs* Average 

(Btu/bu) Btu/gal

Seed 3,617 2,428

Fertilizer: 

 Nitrogen 2,482 1,666

 Phosphorus 1,313 881

 Potash 1,721 1,155

Direct Energy: 

 Diesel 16,280 10,928

 Gasoline 4,782 3,210

 Propane 1,817 1,220

 Electricity** 1,330 893

 Natural Gas 1,607 1,079

Ag. Chemical Application: 

 Herbicides 4,368 2,932

 Insecticides 55 37

Lime 506 340

Total Fossil Energy for Agriculture 39,878 26,769

 * Inputs are adjusted by energy efficiency factors. 

 **Assumes 70 percent of electricity generated from fossil sources. 

8 
plants was estimated to be 6,393 Btu/bushel, which is equivalent to about 4,291 Btu per gallon of 

biodiesel. The estimation was based on a distance of 50 miles for trucking soybeans from a 

distribution center to the soybean crusher/biodiesel plant. 

Estimating Energy for Oil Crushing and Biodiesel Conversion 

The production of biodiesel from soybeans occurs in two stages: the soybeans are first treated to 

remove the oil, and then the soybean oil is converted into biodiesel. The first stage, the removal 

of the oil from the soybean, is often called crushing, and the most common method used to 

convert the oil into biodiesel is a process known as transesterification. Since actual industry 

 data for soybean crushing and biodiesel production were not available, this study had to develop 

a generic model to estimate the energy required to crush soybeans and produce biodiesel using 

transesterification. The energy requirements for soybean crushing and transesterification were 

estimated using a computer model utilizing chemical process engineering and cost engineering 

technology that were developed by USDA’s Agricultural Research Service (Haas et al.). The 

model measures the electrical and thermal energy inputs required for a joint facility that 

combines a soybean processing plant with a biodiesel conversion plant producing 9.8 million 

gallons of biodiesel, 151,515 tons of soybean meal, 9,000 tons of soybean hulls, and 4,380 tons 

of crude glycerin. The model provides a blueprint of a biodiesel plant based on the best 

information available, but it does not represent an actual plant, since actual industry data were 

not used.

Oil Extraction From Soybeans

The separation of the soybean into oil and soybean meal, which is generally referred to as 

crushing, can be done by crushing using mechanical extruders, but more commonly the oil is 

extracted from the soybeans using chemical hexane extraction (figure 2). A soybean processing 

facility uses energy in the form of electricity to power motors and provide lighting. Natural gas 

and process steam are used to provide heat for drying. The model used in this analysis allows 

the plant to generate its own steam from natural gas with a boiler efficiency of 80 percent. Thus, 

the energy value for steam is incorporated in the energy value of natural gas used to generate the 

required steam. Soybeans entering the process are first cleaned and then heated and dried to 

obtain a 10-percent moisture content (Erickson, 1995). Then the beans are cracked into several 

pieces by passing them through mechanical rolls. The soybean hulls, which account for about 8 

percent of the soybean, are removed by aspiration. The hulls may be blended with the soybean 

meal that is later extracted in the process or they may be further treated by toasting and grinding 

and sold as animal feed. The dehulled beans or meats are conditioned by heating, cut into flakes, 

and fed to the oil extraction unit where the oil from the beans is dissolved with hexane. The oil 

and hexane mixture is treated with steam to separate the hexane from the oil. Once the hexane is 

removed, it is recycled for additional processing. Hot air and cooling water are used in the final 

heating and drying of the oil. The crude soybean oil is degummed and may be deodorized, 

bleached, and neutralized. The oil-depleted, dried soybeans are ground to a uniform size to 

make soybean meal, and in some cases, the hulls are blended with the soybean meal. The 

combined total thermal and electric energy required for preparing the soybeans, extracting the oil 

from the beans, and drying the soybean meal is 23,151 Btu per gallon of biodiesel (table 3). 

9 
Conversion of Soybean Oil Into Biodiesel 

The conversion of soybean oil into biodiesel is done by reacting the oil with an alcohol, usually 

methanol, and a catalyst, such as sodium hydroxide, in large reactors. After the soybean oil, 

methanol, and catalyst have reacted, the resulting mixture is centrifuged to remove excess 

methanol, glycerin, and other impurities. After the centrifuge step, the mixture is then washed 

with a water acid solution and dried to become a methyl ester, which is commercially known as 

biodiesel (figure 2). The stream of methanol, glycerin, and other impurities is then treated with 

a small amount of acids and bases to remove any remaining fatty acids. The remaining material 

is then distilled to recover the methanol and most of the water. The excess methanol and water 

are recovered and reused to avoid waste and reduce input costs. The crude glycerin is often sold 

to companies that refine the glycerin to be used in the production of various other products, 

including fiberglass resin, cosmetics, pharmaceuticals, liquid laundry detergents, soaps, deicers, 

and antifreeze. Electrical energy is used to drive the pumps, centrifuges, and mixers, while 

thermal energy is needed in the distillation column to recover the excess methanol and remove 

the final rinse water from the biodiesel. Thermal energy is also used to heat the soybean oil to 

accelerate the conversion process. The conversion of the soybean oil into biodiesel, the recovery 

of the excess methanol, and the treatment of the glycerin requires 18,772 Btu per gallon of 

biodiesel (table 3). 

10 
Figure 2  Soybean crushing and biodiesel conversion 

11 
Table 3 – Fossil energy requirements for soybean crushing and conversion before allocating 

coproduct values, per gallon of biodiesel 

 

Inputs 

Equivalent 

Energy 

(Btu/gal) 

Adjusted 

Equivalent 

Energy* 

(Btu/gal) 

Source 

Soybean crushing: 

 Electricity** 2,738 6,124 ARS 

 Natural Gas/Steam 14,532 15,460 ARS 

 Hexane -- 1,567 Huo et al. 

Total fossil energy for crushing 23,151 

Biodiesel conversion: 

 Electricity 439 981 ARS 

 NG/Steam 3,551 5,840 ARS 

 Methanol 7,193 10,633 Huo et al. 

 Sodium Methoxide -- 1,256 Huo et al. 

 Sodium Hydroxide -- 24 Huo et al. 

 Hydrochloric Acid -- 38 Huo et al. 

Total fossil energy for conversion 18,772 

* Inputs are adjusted by energy efficiency factors. **Assumes 70 percent of electricity generated from fossil sources, which is adjusted for 

generation and line losses. 

Biodiesel Transport 

The GREET model was used to estimate the energy required for transporting biodiesel. 

Transporting biodiesel to marketing outlets requires 8,767 Btu per million Btu of biodiesel. This 

is equivalent to 1,027 Btu per gallon of biodiesel transported. The estimation was based on the 

total distance of 335 miles using a combination of truck, barge, and rail. It required a distance of 

about 32 miles for truck, 42 miles for barge, and 232 miles for rail to transport biodiesel from the 

plant to a distribution center, and another 30 miles by truck to get it to its final destination. 

Calculating Energy Coproduct Values

The energy used to produce the meal portion of the soybean and the crude glycerin that is 

produced during the transesterification stage must be excluded from the LCI. Several allocation 

methods can be used to estimate the energy value of coproducts. The Sheehan et al. study used a 

12 
mass-based allocation method, which simply allocates energy to the various coproducts by their 

relative weights. In order to provide a consistent comparison to the original Sheehan et al. study, 

we also use the mass-based allocation method (figure 3). Soybean crushing produces oil, meal, 

Figure 3 ─ Mass-based energy allocation for biodiesel coproducts 

Agriculture, Bean 

transport, Crushing

Oil transport, 

Biodiesel Conversion

E1

E2

Oil

Meal

Biodiesel

Glycerol

Biodiesel transport

20.6%

82.4%

17.6%

E3

Biodiesel

100%

79.4 %

Waste

Waste

gum, and waste material. USDA ERS (2009) reported a U.S. average oil yield of 11.39 pounds 

per bushel of soybeans, a soybean meal yield of 43.9 pounds per bushel, and a hull yield 

of 3.27 pounds per bushel in 2002/2003. Excluding the hulls and waste material, 20.6 percent of 

the total energy used for soybean agriculture, soybean transport, and crushing is allocated to the 

oil used to make biodiesel, and 79.4 percent is allocated to the meal (figure 3). 

Crude degummed soybean oil contains a small amount of unsaponifiable matter and free fatty 

acids that must be removed because they are detrimental to the transesterification process 

(Sheehan et al., pp 145). The free fatty acids can turn into soap when transesterified, resulting in 

more difficult phase separation of the methyl ester and glycerin. The crude degummed oil is 

treated with sodium hydroxide to obtain dry refined oil, with a yield of about 96 percent 

(Sheehan et al., pp 146). The other 4 percent is considered waste. Following transesterification, 

the proportion of refined biodiesel to crude glycerin (with a purity of about 80 percent) is 82.4 

percent biodiesel and 17.6 percent crude glycerin. Therefore, 82.4 percent of the total energy 

used to convert degummed soybean oil into biodiesel is allocated to biodiesel and 17.6 percent is 

allocated to crude glycerin (figure 3). In addition, the coproduct energy value of crude glycerin 

must be deducted from soybean agriculture, crushing, and soybean transport, so that f1 in 

equation (2) = 0.170 = (0.2060.824), and f2 = 0.824. All the energy used to transport biodiesel 

is allocated to biodiesel (figure 3). 

13 
Results 

Combining the energy input estimates from the four subsystems completes the base case lifecycle assessment for biodiesel (table 4). As discussed above, the energy requirements for 

producing the biodiesel coproducts (i.e., soybean meal and crude glycerin) have been removed 

from the biodiesel inventory. The energy use estimates in table 4 are adjusted by energy 

efficiency factors (appendix table 2). All estimates of electricity generation were based on 

weighted average of all sources of power used in the United States, including coal, natural gas, 

nuclear, and hydroelectric. Electricity use only includes electricity generated from fossil 

sources, which on a natural average equals 70 percent. 

After adjusting the inputs by energy efficiencies and allocating energy by coproducts, the total 

energy required to produce a gallon of biodiesel is 25,696 Btu (table 4). Biodiesel conversion 

uses the most energy, accounting for about 60 percent of the total energy required in the lifeTable 4 – Base case energy use for biodiesel and FER with coproduct allocation and 

adjusted by energy efficiency factors 

 Fossil Energy Use 

 (Btu/gal of Biodiesel) 

Life-Cycle Inventory 

Total Biodiesel 

fraction1

Agriculture 26,769 4,544 

Soybean transport 4,291 728 

Soybean crushing 23,151 3,930 

Biodiesel conversion 18,772 15,467 

Biodiesel transport 1,027 1,027 

Total Energy Input for Biodiesel 

Adjusted for Coproducts 25,696 

Biodiesel Total Energy Output 117,093 

Net Energy Value 91,397 

Fossil Energy Ratio (FER) 4.56 1

 Coproducts are allocated as shown in figure 3.

cycle inventory. Soybean agriculture accounts for 18 percent of the total energy requirements, 

followed by soybean crushing, which requires almost 15 percent of the total energy. The net 

energy value (i.e., biodiesel energy output, minus fossil energy input) is about 91,000 

Btu per gallon. The estimated FER of biodiesel is 4.56, which is about 42 percent higher than 

the FER reported by Sheehan et al. 

14 
A major reason for this improvement is that the soybean crusher modeled for this study more 

accurately measured the energy used by a modern facility. Soybean crushing facilities that have 

been built in recent times are far more energy efficient than the older plant used by Sheehan et al. 

In addition, since 2002, EPA has required soybean plants to limit their hexane use, thus the 

amount of hexane reported by Sheehan et al. had to be adjusted to reflect the new industry 

standard (EPA, 2001). The new hexane energy value that was used in this study is one-half of 

that reported by Sheehan et al. Overall, the energy required for crushing fell from 9,321 Btu to 

3,930 Btu per gallon of biodiesel, about a 58-percent reduction (figure 4). The reduction in the 

crushing energy is primarily due to a reduction in the electricity and natural gas/steam inputs. 

The fossil energy inputs for soybean agriculture fell from 7,681 Btu to 4,544 Btu (41 percent 

reduction) per gallon of biodiesel (figure 4). This reduction is primarily due to less diesel, 

gasoline, fertilizer, and chemical usage. A likely reason for the decrease in fuel use is the 

increased adoption of less intensive tilling practices by soybean farmers. The lower chemical use 

in 2002 is partially related to the adoption of GE soybeans; however, differences in weather and 

other factors unrelated to energy efficiency can cause annual variation in chemical use. 

Figure 4 – Comparing energy requirements for selected biodiesel subsystems and total lifecycle energy requirements between this study and Sheehan et al. 

 

The energy required for transesterification estimated in this study was about 12 percent lower 

than the estimate reported by Sheehan et al. (figure 4). The fossil energy for electricity 

decreased and methanol usage decreased; however, natural gas and steam usage slightly 

increased. Overall, the total life-cycle energy required for biodiesel fell from 36,416 Btu to 

25,696 Btu per gallon. 

The Effects of Adding Inputs to the LCI

Figure 5 shows the effects of adding secondary energy inputs to the LCI that were not included 

in Sheehan et al. to determine how they affect the overall results. Hill et al. estimated the energy 

associated with manufacturing farm machinery to be 7,547 Btu per bushel (5,066 Btu/gal of 

7.7

9.3

17.7

36.4

4.5 3.9

15.5

25.7

0

10

20

30

40

Agriculture Crushing Conversion Total

Thousands Btu/gal of BD

Sheehan et al.

Updated

36

38

35

36

37

38

39

Yield

Bu/acre

15 
biodiesel). Adding the biodiesel share of this energy to soybean production reduces the base case 

FER of 4.56 to 4.41. Hill et al. also estimated the energies associated with building materials193 Btu per bushel (129 Btu/gal of biodiesel) for a crushing plant and 100 Btu per bushel (67 

Btu/gal of biodiesel) for a biodiesel conversion plant. Adding the biodiesel share of energy 

related to building materials lowered the FER to 4.54. If the input energy for both agricultural 

machinery and building material were added to the inventory, FER would decline to 4.40, still 

considerably higher than the 3.2 FER reported by Sheehan et al. 

The Effect of Adding Lime to the LCI 

Our base case LCI included lime unlike the Sheehan et al. inventory that omitted lime. Lime is 

added to soil periodically, and the annual lime application rates reported in table 1 are adjusted 

by average years between applications. 

Figure 5 – Effect on fossil energy ratio from adding the energy from secondary energy 

inputs to the life-cycle inventory 

4.56

4.41

4.54

4.40

012345

Base

Base + Ag. Mach.

Base + Build. Mat.

Base + Ag. Mach. + Build. Mat.

FER

Since farmers do not apply lime every year and some acreage never receives lime, the adjusted 

annual average lime application rate is relatively small. Lime use only accounts for 506 Btu per 

bushel of soybeans and lowers the FER by only about 0.22 percent. Therefore, including lime in 

the Sheehan et al. inventory would not have changed the results significantly. 

Effect of Oil Transport 

The generic biodiesel plant modeled in this study combined an oil crushing facility with a 

biodiesel conversion plant at the same location. Soybeans are shipped to the plant and crushed 

into oil that is converted to biodiesel onsite; hence oil transport was not included in the baseline 

inventory. There are many biodiesel plants in the industry that do not have crushing capability, 

so they must purchase oil and have it transported to their plant. The model used by Sheehan et 

16 
al. separated the crusher from the biodiesel conversion facility, so their inventory included the 

energy required to transport the oil to the biodiesel plant, which was 843 Btu per gallon of 

biodiesel for 571 miles. When adding this energy to our inventory, the FER declines to 4.41 

compared to the baseline result of 4.56. 

Effect of Soybean Yield 

Even though yields have been higher in recent years, yield data for year 2002 were used to 

calculate FER in this study to correspond to the 2002 ARMS agricultural input data. Yield plays 

a critical role in the FER calculation because as soybean yields increase over time, the FER of 

biodiesel is also expected to increase. The USDA projects soybean yield to increase annually by 

0.4 to 0.5 bushel/acre through the year 2017 (USDA, Office of the Chief Economist-a). For 

every 1 bushel increase in soybean yield, FER increases by about 0.45 percent. Holding all other 

variables constant, the FER of soybean biodiesel is estimated to reach 4.69 in the year 2015, 

when soybean yield is projected to increase to 45.3 bushels per acre. This is about a 3- percent 

increase compared to the 2002 FER estimate. 

Summary and Conclusion 

The fossil energy ratio (FER) of biodiesel is 4.56 based on data from 2002 soybean production. 

This is a significant improvement over the 1998 Sheehan et al. study that reported a FER of 3.2. 

A major reason for this improvement is that the soybean crusher modeled for this study more 

accurately measured the energy used by a modern facility. Soybean crushing facilities that have 

been built in recent times are far more energy efficient than the older plant used by Sheehan et al. 

In addition, improved soybean yields and overall less energy used on the farm helped increase 

the energy balance of biodiesel. When comparing the 2 study years (1990 and 2002), less 

fertilizers and pesticides were applied in the latter year. The lower chemical use in 2002 can 

partially be explained by the adoption of GE soybeans that resulted in reduced pesticide use. 

However, differences in weather and other factors unrelated to energy efficiency may have also 

partially been responsible for the lower farm energy estimates in 2002. 

The life-cycle inventory used for this study was constructed to resemble the Sheehan et al. study 

in order to make comparisons between the two time periods. To be consistent with Sheehan et 

al., secondary inputs such as building materials and farm machinery were not included in the 

base case inventory. However, the results show that the FER of biodiesel changes very little 

when adding secondary inputs to the life-cycle inventory. The model used to estimate the energy 

required to convert soybean oil into biodiesel represents a soybean processing plant combined 

with a transesterification unit with an annual capacity of 9.8 million gallons per year. Although 

plants under 10 million gallons are quite common, there has been a recent trend in the industry 

towards larger plants. Larger plants with more capital investment would be expected to be more 

energy efficient. 

Finally, the results from this research suggest that the FER of biodiesel will continue to improve 

over time. This improvement will occur because increases in soybean yields are expected to 

continue and for every one bushel per acre increase in soybean yield, the FER increases by 0.45 

percent. In addition, the agricultural sector, along with the biodiesel industry, will likely 

17 
continue to make energy efficiency gains in order to lower production costs. In the future, as the 

United States develops its renewable energy resources, more non-fossil energy will be included 

in the biodiesel life-cycle inventory; for example, more electricity may be generated from 

biomass, wind, and solar power, and more farm equipment may use biofuels. Replacing fossil 

energy with renewable energy over the life cycle could also significantly increase the energy 

balance of biodiesel over time. 

References 

American Methanol Institute. AMI. Properties of Fuels. Available at 

http://www.methanol.org/pdf/FuelProperties.pdf. Assessed 2009. 

Argonne National Laboratory. The Greenhouse Gases, Regulated Emissions, and Energy Use in 

Transportation (GREET) Model. Version 1.8b. Argonne, IL 2008. Available at: 

http://www.transportation.anl.gov/modeling_simulation/GREET/index.html

Ash, M. and E. Dohlman. Oil Crops Situation and Outlook Yearbook. Economic Research 

Service, United States Department of Agriculture. OCS-2007, May 2007. Available at 

http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1289. 

Ash, M., Livezey, J., and E. Dohlman. Soybean Backgrounder. Economic Research Service, 

United States Department of Agriculture. OCS-2006-01, April 2006. Electronic Outlook 

Report from the Economic Research Service. Available at 

http://www.ers.usda.gov/publications/OCS/apr06/OCS200601/OCS200601_lowres.pdf

Energy Information Administration. Electricity flow, 2007. Annual Energy Review, 2007. 

Annual Energy Review, 2007. DOE/EIA-0384 (2007). U.S. Department of Energy. 

http://www.eia.doe.gov/emeu/aer/pdf/pages/sec8_3.pdf, accessed 5/21/2008 

Erickson, D.R. 1995. Overview of modern soybean processing and link between processes. In 

Practical handbook of soybean processing and utilization, 56-64.Erickson, D. R. ed. 

Champaign,IL: AOCS Press and United Soybean Board. 

Graboski, M. Fossil Energy Use in the Manufacture of Corn Ethanol. Prepared for National 

Corn Growers Association. Unpublished. 

Haas, M. J., McAloon, A.J., Yee, W.C., Foglia, T.A. A Process Model to Estimate Biodiesel 

Production Costs. Bioresource Technology, 97:671-678, 2006. 

Heimlich, R. E., J. Fernandez-Cornejo, W. McBride, C. Klotz-Ingram, S. Jans, and N. Brooks. 

Genetically Engineered Crops: Has Adoption Reduced Pesticide Use? Agricultural 

Outlook, AGO-273/August 2000. Economic Research Service, United States Department 

of Agriculture. Available at: http://usda.mannlib.cornell.edu/reports/erssor/economics/aobb/2000/ao273.pdf 

Hill, J., E. Nelson, D. Tilman, S. Polasky, and D. Tiffany. Environmental, Economic, and 

Energetic Costs and Benefits of Biodiesel and Ethanol Biofuels. PNSS. 103(30): 11206-

11210. 2006. 

Huo, H., Wang, M., C. Bloyd and V. Putsche. Life-Cycle Assessment of Energy and Greenhouse 

Gas Effects of Soybean-Derived Biodiesel and Renewable Fuels. United States 

Department of Energy, Office of Energy Efficiency and Renewable Energy. 

ANL/ESD/08-2. 2008. 

18 
Knothe, G., J. H. Van Gerpen, and J. Krahl. The Biodiesel Handbook. Champaign, Ill: AOCS 

Press. 2005. 

Kovach, J., C. Petzoldt, J. Degni, and J. Tette. A Method to Measure the Environmental Impact 

of Pesticides. Cornell University: New York State Integrated Pest Management Program. 

2007. 

Pimentel, D. and Patzek, T. Ethanol Production Using Corn, Switchgrass, and Wood; 

 Biodiesel Production Using Soybean and Sunflower. Natural Resources Research, Vol. 

14, No.1, March 2005. 

Pradhan, A., Shrestha, D. S., J. V. Gerpen, and J. Duffield. The Energy Balance of Soybean Oil 

Biodiesel Production: A Review of Past Studies. Transactions of the American Society of 

Agricultural and Biological Engineers. 51(1): 185-194. 

Shapouri, H., J. A. Duffield and M. Wang. The Energy Balance of Corn Ethanol: An Update. 

U.S. Department of Agriculture, Office of Energy Policy and New Uses. Agricultural 

Economic Report No. 813. 7/2002 

Sheehan, J., V. Camobreco, J.A. Duffield, M. Graboski, and H. Shapouri. 1998. Life-cycle 

Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus. A Joint Study 

Sponsored by U.S. Department of Agriculture and U.S. Department of Energy. 

NREL/SR-580-24089 Golden, CO: National Renewable Energy Laboratory. U.S. 

Department of Energy, 5/1998. 

Thorson, T. (Pesticide Expert). Personal communication. United States Department of 

Agriculture, National Agricultural Statistics Service. 2008. 

U.S. Environmental Protection Agency. A Comprehensive Analysis of Biodiesel Impacts 

 on Exhaust Emissions: Draft Technical Report. Assessment and Standards Division, 

 Office of Transportation and Air Quality. Report. EPA420-P-02-001. 11/2002. 

U.S. Environmental Protection Agency. Integrated Risk Information System. Available at 

http://www.epa.gov/iris/subst/0057.htm

U.S. Environmental Protection Agency. 2001. Rule and Implementation Information for 

Vegetable Oil Production; Solvent Extraction. Technology Transfer Network Air Toxics. 

Available at http://www.epa.gov/ttn/atw/vegoil/vegoilpg.html 

U.S. Department of Agriculture, Agricultural Research Service. Unpublished data provided by 

the Fats, Oils and Animal Coproducts Research Unit, 2008. 

U.S. Department of Agriculture, Economic Research Service (a). Farm Business and 

 Household Survey Data: Customized Data Summaries From 

 ARMS. Tailored Reports, 2002. Economic Research Service. Available at: 

 http://www.ers.usda.gov/Data/ARMS/app/Crop.aspx

U.S. Department of Agriculture, Economic Research Service. Oil Crops Yearbook 2009. 

 Available at: 

http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID1290

U.S. Department of Agriculture, Economic Research Service (b). Soybean Production Costs 

and Returns from the 2002 ARMS. Special Tabulations. Economic Research Service. 

Available at: http://www.ers.usda.gov/Briefing/ARMS/Access.htm. 

U.S. Department of Agriculture, Economic Research Service. Agricultural Biotechnology: 

Adoption of Biotechnology and Its Production Impacts. 2007. Available at: 

http://www.ers.usda.gov/Briefing/biotechnology/chapter1.htm. Accessed on: 05.28.08 

19 
U.S. Department of Agriculture, Economic Research Service. Agricultural Resources and 

Environmental Indicators: Soil Management and Conservation, 2003, Chapter 4.2, p.33. 

Available at 

http://www.ers.usda.gov/publications/arei/ah722/arei4_2/AREI4_2soilmgmt.pdf 

U.S. Department of Agriculture, National Agricultural Statistics Service. Agricultural Statistics 

2005. United States Government Printing Office, Washington D.C. 2005. 

U.S. Department of Agriculture, National Agricultural Statistics Service. Agricultural Chemical 

Usage-Field Crops Summary, Issues 1990-2005. Available at 

http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1560 

U.S. Department of Agriculture, Office of the Chief Economist (a). USDA Agricultural 

Projections to 2017. World Agricultural Outlook Board, Long-term Projections Report, 

OCE-2008-1, February 2008. 

U.S. Department of Agriculture, Office of the Chief Economist (b). World Agricultural Supply 

and Demand Estimates. WASDE 469. April 9, 2009. World Agricultural Outlook Board, 

Office of the Chief Economist. Available at 

http://www.usda.gov/oce/commodity/wasde/index.htm. 

Vigon, B. W., Tolle, D. A., Cornaby, B. W., Latham, H. C., Harrison, C. L., Boguski, T. L., R. G. 

Hunt and J. D. Sellers. Life-Cycle Assessment: Inventory Guidelines and Principles. 

Washington D.C. & Cincinnati: United States Environmental Protection Agency, Office 

of Research and Development. (EPA/600/R-92/245). 1993. 

Wang, M. Q. and H. S. Huang. A Full Fuel-Cycle Analysis of Energy and Emissions Impacts of 

 Transportation Fuels Produced from Natural Gas. Center for Transportation Research, 

Argonne National Laboratory. ANL/ESD-40. December 1999. 

Woerfel, J. B. Chapter 6: Extraction, Practical handbook of soybean processing and utilization, 

65-92.Erickson, D. R. ed. Champaign,IL: AOCS Press and United Soybean Board. 1995. 

20 
Appendix 

Appendix Table 1 – Energy coefficients used to convert inputs into British thermal units 

(Btu) 

Inputs Energy Value Sources 

Fuel Inputs Low Heating Value 

Diesel (Btu/gal) 128,450 Huo et al. 

Gasoline (Btu/gal) 116,090 Huo et al. 

Propane(Btu/gal) 84,950 Huo et al. 

Natural Gas (Btu/cft) 983 Huo et al. 

Electricity (Btu/kWh) 3,412 Huo et al. 

Material Inputs 

Nitrogen (Btu/lb) 22,136 Hill et al 

Phosphorus (Btu/lb) 3,944 Hill et al. 

Potassium (Btu/lb) 2,563 Hill et al. 

Lime (Btu/lb) 53.72 Graboski 

Seeds (Btu/lb) 2,024 Sheehan et al. 

Herbicide (Btu/lb) 137,191 Hill et al. 

Insecticide (Btu/lb) 139,772 Hill et al. 

Methanol (Btu/lb) 9,750 American Methanol 

Institute 

 Appendix Table 2 -- Life-cycle energy efficiency factors for fossil fuels and electricity 

Inputs Life-Cycle Efficiency 

percent 

Diesel 84.3 

Gasoline 80.5 

Propane 89.8 

Natural Gas 94.0 

Steam 60.8 

Electricity 31.3 

Methanol 67.7 

 

Source: Shapouri et al.; Energy Information Administration; United State Department of 

Agriculture, Agricultural Research Service; and Wang and Huang.

21 
Glossary 

Allocation Method ─ Rules to determine the fraction of total input energy that is assigned to 

each coproduct. For example, both biodiesel and glycerin are produced during the 

transesterification process, but the energy used to produce the two products cannot be easily 

delineated. Therefore an allocation method has to be used, such as a mass-based rule that 

allocates energy to the various coproducts by their relative weights. 

ARMS  USDA's Agricultural Resource Management Survey (ARMS) is sponsored jointly by 

the Economic Research Service (ERS) and the National Agricultural Statistics Service (NASS). 

ARMS began in 1996 as a synthesis of the former USDA cropping practice, chemical use, and 

farm costs and returns surveys, which dated back to 1975. It is USDA's primary source of 

information on the financial condition, production practices, resource use, and economic wellbeing of America's farm households. http://www.ers.usda.gov/data/arms/GlobalAbout.htm#Use

British Thermal Units (Btu) ─ British thermal units are widely used in the United States to 

describe the heat value or energy content of fuels and other types of energy. One Btu is 

equivalent to 1,055 joules, which is an energy unit in the international system of weights and 

measures. 

Catalyst ─ A substance that enables a chemical reaction to proceed usually at a faster rate or 

under different conditions (as at a lower temperature) than otherwise possible. 

Centrifuge ─ A process of separating liquids with different specific gravities by rotating the 

fluid at high speed. 

Coproduct ─ When a production process results in two or more products, the products are called 

coproducts. For example, a soybean processing plant crushes soybeans to obtain two marketable 

coproducts (i.e., soybean oil and soybean meal). 

Degummed Soybean Oil ─ Soybean oil after removing phosphotides and some unsaponifiable 

matter commonly known as gums. 

Dehulled Beans or Meats ─ That part of the soybean remaining after removing the hull. The 

hull is the skin of the soybean, which is removed to facilitate solvent extraction of the oil and 

improve protein content of the meal. 

Direct Energy Inputs ─ Inputs in the form of energy, such as gasoline, diesel, natural gas, and 

electricity. Inputs that depend on energy for their production, such as fertilizers and pesticides, 

are indirect energy inputs. 

Energy Balance of a Biofuel ─ An energy life-cycle assessment that measures the fossil energy 

required to produce a biofuel relative to its energy output value. 

Energy Efficiency Factor ─ A coefficient used to account for the energy required to bring a raw 

energy resource from the environment to its final useable form. For example, for every unit of 

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electrical energy produced, it takes on average 3.2 units of energy to get that energy into its final 

form and transport it to its final destination. Therefore, 3.2 is the energy efficiency factor for 

electricity, and the electrical energy used to produce a product must be multiplied by this factor 

to account for the total energy associated with electricity use. 

Energy Life-Cycle Assessment ─ A life-cycle assessment that focuses just on the energy inputs 

and outputs of a product. 

Environmental Impact Quotient (EIQ) ─ A measurement that estimates the environmental 

impacts of a pesticide taking into account several environmental variables, including fish 

toxicity, bird toxicity, bee toxicity, and leaching potential. 

Fatty Acids  Fats or triglycerides, which are the primary constituents of vegetable oils and 

animal fats. When using transesterification, the triglycerides are transformed to esters and crude 

glycerin. The esters become biodiesel and the glycerin can be further processed to make other 

products. 

Free Fatty Acids ─ Fatty acid groups that have broken off from the vegetable oil triglyceride 

molecule. Unless properly accounted for, free fatty acids consume catalyst needed for 

transesterification, lowering yield, increasing the reaction time, or potentially stopping the 

reaction altogether. Feedstocks with high free fatty acid levels will often be pretreated to 

remove free fatty acids before transesterification. 

Feedstock ─ Raw material used in making an energy product. For example, biodiesel can be 

made from various feedstocks, including soybean oil, animal fat, and recycled cooking oil. 

Fossil Energy ─ Energy derived from fossil fuel, which includes petroleum oil, coal, and natural 

gas. 

Fossil Energy Ratio (FER) ─ The energy output of a biofuel divided by the life-cycle energy 

required to produce the product. The FER only includes fossil energy in the denominator, and it 

is often the measurement used to quantify the energy balance of a biofuel. 

Genetically Engineered (GE) Soybeans ─ A soybean variety that has been genetically modified 

to make it more resistant to herbicide applications, primarily glyphosate, commercially known as 

Roundup. GE soybeans were developed to survive the application of glyphosate that previously 

would have destroyed the crop along with the targeted weeds. 

Glycerin or Glycerol ─ An organic compound present in all animal and vegetable fats that is 

produced along with biodiesel when using the transesterification production process. 

Historically, refined glycerin has been a product of the commercial soap industry; however, a 

synthetic glycerin is also produced on a commercial scale by the petroleum industry. 

Commercial glycerin is found in many products, including solvents, sweeteners, cosmetics, 

liquid soaps, candy, liqueurs, and dynamite. 

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GREET Model ─ The Greenhouse Gases, Regulated Emissions, and Energy Use in 

Transportation (GREET) Model was developed by Argonne National Laboratory, U.S. 

Department of Energy. It fully evaluates life-cycle energy and emission impacts of advanced 

vehicle technologies and new transportation fuels. 

http://www.transportation.anl.gov/modeling_simulation/GREET/index.html

Life Cycle ─ Consecutive and interlinked stages of a product system, from raw material 

acquisition or generation from natural resources to final disposal (ISO 14040). The life cycle of 

soybean biodiesel is assumed to start from the beginning of the soybean production and end with 

the delivery of the biodiesel to a gas station or the point of the final use. 

Life-Cycle Assessment (LCA) ─ Also known as life-cycle analysis, it is a technique to assess or 

measure certain aspects of a product over its entire life cycle. Life-cycle assessments are most 

often used to assess the environmental aspects of a product, but LCAs can also be used to 

measure the social impacts of a product. 

Life-Cycle Inventory (LCI) ─ The database that contains the amounts of all inputs and outputs 

of processes that occur during the life cycle of a product. The LCI is typically organized by a set 

of subsystems (e.g., biodiesel includes a feedstock subsystem and a conversion subsystem). The 

LCI sets boundaries for each subsystem to avoid unnecessary data collection. 

Methyl Ester ─ Biodiesel is called a methyl ester if the alcohol used for transesterification is 

methanol. 

Net Energy Value (NEV) ─ The energy content of 1 gallon of biodiesel minus the life-cycle 

fossil energy required to produce 1 gallon of biodiesel. A biofuel has a positive energy balance if 

its NEV is greater than one, and a negative energy balance if the NEV is less than one. 

No-Till ─ A crop residue management (CRM) system that maintains additional crop residue on 

the soil surface through fewer and/or less intensive tillage operations. CRM is generally cost 

effective in protecting soil and water resources and can lead to higher farm economic returns by 

reducing fuel, machinery, and labor costs while maintaining or increasing crop yields. 

Pest Management ─ A set of techniques used to reduce pest populations or prevent their 

detrimental effect on crops and livestock. A pest is any noxious and damaging organism, 

including mites, insects, plant pathogens, and weeds. Pest management techniques can be 

broadly classified into chemical, cultural, and biological. 

Renewability ─ The degree in which a biofuel is renewable. The fossil energy ratio (FER), 

which is the ratio of renewable energy output to fossil energy input, is a measure of renewability. 

Biofuels that use less fossil energy per unit of renewable energy output have a higher degree of 

renewability. 

Secondary Inputs ─ Secondary inputs have no energy value per se, but it requires energy to 

produce them (e.g., building materials used to construct processing plants and farm vehicles used 

for cultivation). These inputs are often excluded from the LCI because they do not provide 

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direct energy to the system and they’re difficult to quantify. Energy estimates for secondary 

inputs are generally very small, so their exclusion from the inventory has little effect on the 

LCA. 

Soybean Crusher ─ A generic term used for a plant that primarily processes soybeans into two 

products: soybean meal and soybean oil. 

System Boundaries ─ Limits set in the life-cycle inventory (LCI) to prevent boundless 

production systems and unnecessary data collection. Whether to include or exclude energy used 

beyond direct inputs, such as energy embodied in labor, building materials, and manufacturing 

equipment, depends on several factors, including goal and scope of the LCA, availability of data, 

reliability of data, time and cost of collecting the data, and the extent to which the inclusion will 

make difference in the final result. 

Thermal Energy ─ The energy required for heating, for example, the heat generated from 

natural gas to dry soybeans. 

Transesterification ─ A process for producing alkyl esters (biodiesel) by reacting a vegetable 

oil or animal fat with an alcohol, usually ethanol or methanol. This reaction also results in the 

production of crude glycerin. 

Unsaponifiable Matter ─ Non-triglyceride part of oil and fat that does not convert into 

soap. It is removed from the oil because it is detrimental to the transesterification 

process. 

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on 

the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial 

status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or 

because all or a part of an individual's income is derived from any public assistance program. (Not all 

prohibited bases apply to all programs.) Persons with disabilities who require alternative means for 

communication of program information (Braille, large print, audiotape, etc.) should contact USDA's 

TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination write to 

USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-

9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider 

and employer.